<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>圆角边框</title>
    <style>
        body div:nth-child(1){
            /*半圆形*/
                    /*利用border-radius属性制作半圆形的两个要点*/
                    /*制作上半圆或下半圆时，元素的宽度是高度的2倍，而且圆角半径为元素的高度值*/
                    /*制作左半圆或右半圆时，元素的高度是宽度的2倍，而且圆角半径为元素的宽度值*/
            background: red;
            width: 200px;
            height: 100px;
            /*border-top-left-radius: 200px;*/
            /*border-top-right-radius: 150px;*/
            /*border-bottom-right-radius: 100px;*/
            /*border-bottom-left-radius: 50px;*/
            /*border-radius:200px 150px 100px 50px ;*/
            border-radius: 100px 100px 0px 0px;
        }
        body div:nth-child(2){
            margin-top: 20px;
            background: red;
            width: 200px;
            height: 100px;
            border-radius: 0px 0px 100px 100px;
        }
        body div:nth-child(3){
            margin-top: 20px;
            background: red;
            width: 100px;
            height: 200px;
            border-radius: 100px 0px 0px 100px;
        }
        body div:nth-child(4){
            margin-top: 20px;
            background: red;
            width: 100px;
            height: 200px;
            border-radius: 0px 100px 100px 0px;
        }

    </style>
</head>
<body>
<div>

</div>
<div></div>
<div></div>
<div></div>
</body>
</html>